As used in the specification, for a cutting insert in hand, the term "rake surface angle" at a section passing through a point anywhere along one of its cutting edges is the angle between the cutting edge's associated rake surface and a plane parallel to the cutting insert's lower surface whilst the term "relief flank surface angle" at a section passing through a point anywhere along one of its cutting edges is the angle between cutting edge's relief flank and a plane normal to the cutting insert's lower surface.
Against this, for a cutting insert mounted in a milling toolholder, the term "radial rake angle" at a section passing through a point anywhere along a side cutting edge is the angle between its associated rake surface and a radius with respect to the milling cutter's rotary axis whilst the term "axial rake angle" at a section passing through a point anywhere along a front cutting edge is the angle between associated rake surface and a projection of the milling cutter's rotary axis onto that section.
And, in a similar manner, for a cutting insert mounted in a milling toolholder, the term "radial relief angle" at a section passing through a point anywhere along a side cutting edge is the angle between its associated relief flank and the tangent to the circular path generated by that point whilst the term "axial relief angle" at a section passing through a point anywhere along a front cutting edge is the angle between its associated relief flank and a plane perpendicular to the milling cutter's rotary axis.
A light metal workpiece is typically provided in a near net shape which requires a single pass of minimal depth-of-cut chip removing combined with finishing operation to arrive at its desired highly smooth final net shape. Such finishing is achieved by a milling cutter having and front cutting edges acting as wipers whose length are only slightly longer than the intended feed per revolution and, therefore, typically in the order of about 2-3 mm. In addition, for effective chip removal from light metal workpieces, a milling cutter is required to present, on the one hand, high shear axial and radial rake angles which are also useful for curling up cut chips which can then be readily evacuated during a high speed cutting operation and, on the other hand, high axial and radial relief angles. Typical values for radial and axial rake angles are about 20.degree. while typical values for radial and axial relief angles are about 12.degree..
Up to the present time, the high axial and radial rake and relief angles required for machining light metal workpieces have been provided by a so-called double positive milling cutter, for example, as described in Applicant's U.S. Pat. No. 5,207,538 to Satran, in which cutting inserts are suitably axially inclined and radially disposed, the downside of which being a weakening of the milling toolholder and an increase in at least the milling cutter's axial runout due to tolerances of its insert receiving pockets. Thus, such milling cutters are unable to achieve highly smooth surfaces which are thereafter obtained by subsequent grinding operations.
EP 0 269 103 A3 describes a cutting insert for machining light metal workpieces having a square insert body with an upper surface and four symmetrical nose-like cutting corners. Each nose-like cutting corner has a pair of concave main cutting edges rising up from the upper surface and meeting at a chamfered corner cutting edge parallel and elevated relative to the upper surface. An operative corner cutting edge serves as a front cutting edge whilst one of its adjacent main cutting edges provides an entrance angle of 45.degree. enabling fairly deep depth-of-cut 45.degree. shouldering or finishing operations. Apart from the insert's limited applications, highly smooth finishing operations are hardly achievable due to the fact that its front cutting edges are not supported and precisely positioned by corresponding support surfaces oppositely disposed thereto for controlling axial runout. In addition, the cutting insert also suffers from the drawback that preparation of its cutting edges entails peripheral grinding of its entire side surfaces since the cutting edges do not-protrude from their respective side surfaces.
In this regard, JP Publication No. 62094903 A describes a compound cutting tool having a brazed-on, ultra hard sintered material, planar cutting corner with cutting edges protruding outwardly from the tool's respective side surfaces for the purpose of preventing dulling of a diamond grinding wheel by the tool's base metal during preparation of the corner's cutting edges.
It is an object of the present invention to provide a new millino cutting insert for machining workpieces of different work material groups and, in particular, of soft "gummy" or light metal materials.